This invention relates generally to ion-exchange material, and more particularly to a volume reduction process for spent radioactive ion-exchange material.
Ion-exchange resins are conventionally used in various nuclear reactor coolant, water makeup, and other systems for removing mineral, metallic, and other impurities from water circulated through a reactor and its associated components. Contrary to practices followed in commercial and domestic ion-exchange systems used for conditioning water, the radioactive resins in the reactor systems usually are not regenerated, and once spent, must be disposed of as radioactive waste.
Various methods have been developed for disposing of the radioactive water and resins. Currently, the spent resins are separated from a resin-water mixture by utilizing a centrifuge which isolates the resins to eventually form a radioactive paste or cake which is disposed of in suitable containers. In those cases where disposal of the water does not take place, it is recycled to the waste process system for further use.
In another system, the resin-water mixture is mixed with a fixing agent, and discharged to an appropriate disposal package. In a third system, the resin-water mixture is discharged into an evacuated drum filled with dry mixture of cement and vermiculite, and equipped with a screen cage insert. The mixture fills the cage and water seeps through the screen into the cement-vermiculite mixture lining the cage, thereby encapsulating the resin in a lining of solidified concrete.
All of these disposal methods are expensive because large volumes of radioactive resin in water must be contained in an appropriate receptacle to eliminate the possibility of later escape to the environment in which the receptacles are buried or stored. Moreover, a substantial effort in terms of time and labor cost, and material cost, is required for the encapsulation of the radioactive waste products in order to comply with prevailing rules and regulations for the disposal of radioactive materials.
In order to minimize the economic costs associated with the disposal, various methods have been attempted to reduce the volume of the spent radioactive ion-exchange materials. One of these methods is to incinerate the ion-exchange material. Incineration does provide a high volume reduction ratio in terms of solid residue. However, the incineration takes place at relatively high temperatures, typically above 1000.degree. C., and in an oxidizing atmosphere. Such operating conditions can produce fine dust entrainment and possibly radioactive volatile formation such as ruthenium tetroxide, RuO.sub.4 and cesium sulfate, Cs.sub.2 SO.sub.4. The removal of the entrained solids and the volatile radioactive gases from the hot exhaust gases is a major and difficult process.
Another volume reduction method attempted was acid digestion. Acid digestion is a form of wet oxidation of solid waste. The radioactive ion-exchange materials are digested with concentrated sulfuric acid and nitric acid. The gases given off are passed through absorbers to remove the sulfur dioxide and nitric oxide. The acid digestion process also provides a high volume reduction ratio for a solid residue. However, acid digestion generates a large volume of contaminated liquid waste, must be operated in glass or glass-lined vessels, and requires similar radioactive treatment of gases given off as does incineration.
Mechanical compaction of the spent radioactive ion-exchange materials is not feasible, since very limited volume reductions are to be expected.